Trends in the development of semiconductor chips show that the area occupied by memory is increasing. If these trends continue, a large part of a System on Chip's overall area will be occupied by memory. Semiconductor technology is scaled down to achieve higher densities of memories. Variations in manufacturing parameters, e.g. variations in number and location of dopant atoms in a channel region of a transistor, increase in accordance with scaling down technology. Correspondingly, threshold voltages of transistors forming memory cells vary increasingly, which makes it difficult to perform stable write and stable read operations.
Besides achieving higher densities of memories, it is generally desirable to save power in applications that use memory that occupies a large amount of chip-area. Scaling the supply voltage is one approach used to save power. A low supply voltage together with variations in manufacturing parameters may lead to memory cell access errors, especially during write operations.